Assessing PSMA PET Uptake in Prostate Cancer Following Radiation

Researchers assessed the kinetics of PSMA PET uptake in prostate cancer lesions following radiation therapy (RT). The results were presented at the 2022 American Society for Radiation Oncology Annual Meeting.

In this single-center retrospective study, presenting author Masatoshi Hotta, MD, PhD, and colleagues analyzed 108 patients with prostate cancer who underwent 1 PSMA positron emission tomography (PET)/computerized tomography scan before RT and at least 1 other scan after RT between November 2016 and July 2021. Lesions with and without residual uptake were assessed for time interval after RT, lesion tissue type (prostate, prostate bed, lymph node, and bone), RT type, baseline uptake intensity, and PSMA-derived tumor volume (PSMA-TV). The analysis consisted of imaging data on 257 irradiated lesions (lymph node, n=126; bone, n=98; prostate, n=25; prostate bed, n=8).

The results showed that residual uptake after RT was presented in 35% of the irradiated lesions. Residual uptake was more commonly observed in the prostate (prostate, 68.0%; bone, 40.8%; prostate bed, 25.0%; lymph node, 24.8%; P<.0001), and this uptake was correlated with higher baseline uptake and lesion size (SUV_max 9.5 vs 6.4; P<.001) and PSMA-TV (1.7 vs 1.0 ml; P=.002) in lesions with residual uptake versus without.

Multivariate logistic regression analysis revealed that shorter time after RT (odds ratio [OR], 0.93; 95% CI, 0.89-0.97), higher baseline SUV_max (OR, 1.07; 1.03-1.11), and lesion in the prostate (OR, 6.84; 2.19-21.3) were independently associated with residual uptake.

“The PSMA PET uptake of irradiated lesion decreases gradually over 1 year, while the uptake in the prostate tends to remain longer than in bone and lymph node lesions,” the researchers concluded.

Source: Hotta M, Nguyen K, Thin P, et al. Kinetics and patterns of PSMA PET uptake in prostate cancer after radiation therapy: a single center retrospective study. Abstract 2501. Presented at the 2022 ASTRO Annual Meeting; October 23-26, 2022; San Antonio, TX.